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Modules for splitting and merging Metafacture pipelines
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/*
 * Copyright 2013, 2014 Deutsche Nationalbibliothek
 *
 * Licensed under the Apache License, Version 2.0 the "License";
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.metafacture.plumbing;

import org.metafacture.framework.FluxCommand;
import org.metafacture.framework.StreamReceiver;
import org.metafacture.framework.annotations.In;
import org.metafacture.framework.annotations.Out;
import org.metafacture.framework.helpers.DefaultStreamPipe;

/**
 * Merges records based on their id. The module compares the id
 * of each record it receives with the one of previous record; if
 * both records have got the same id, then the end-record and
 * start-record events that would normally separate the records
 * are suppressed in the output stream of {@code StreamMerger}.
 * This effectively merges the two records. Of course, this only
 * works if the records which are to be merged follow each other
 * directly.
 *
 * @author Christoph Böhme
 *
 */
@In(StreamReceiver.class)
@Out(StreamReceiver.class)
@FluxCommand("merge-same-ids")
public final class StreamMerger extends DefaultStreamPipe {

    private boolean hasRecordsReceived;
    private String currentId = "";

    /**
     * Creates an instance of {@link StreamMerger}.
     */
    public StreamMerger() {
    }

    @Override
    public void startRecord(final String identifier) {
        assert !isClosed();
        if (!currentId.equals(identifier)) {
            if (hasRecordsReceived) {
                getReceiver().endRecord();
            }
            getReceiver().startRecord(identifier);
            currentId = identifier;
        }

        hasRecordsReceived = true;
    }

    @Override
    public void startEntity(final String name) {
        assert !isClosed();
        getReceiver().startEntity(name);
    }

    @Override
    public void endEntity() {
        assert !isClosed();
        getReceiver().endEntity();
    }

    @Override
    public void literal(final String name, final String value) {
        assert !isClosed();
        getReceiver().literal(name, value);
    }

    @Override
    protected void onResetStream() {
        hasRecordsReceived = false;
        currentId = "";
    }

    @Override
    protected void onCloseStream() {
        if (hasRecordsReceived) {
            getReceiver().endRecord();
        }
        onResetStream();
    }

}